The top part of the diagram shows the logic of on-board robot unit. It shows the sensors interfacing with their respected module which are then inputed to the microcontroller. The microcontroller then uses the Xbee module to transmit data to the Local Control Unit (bottom diagram). On-board will also house the night-vision camera which uses it's own transmitter with 2.4Ghz frequency.
The bottom diagram is the user interface of the robot. Data received will be displayed on the unit once received by the Xbee Rx module and processed by the microcontroller.